Modern RF front ends in portable wireless devices, such as portable wireless communication devices, require minimal size, stable, wideband tuneable oscillators with low operating power and high output power. The frequencies used in commercial systems today are synthesized from off-chip passive resonators, e.g. quartz crystals, with a very high-quality resonance at low frequencies (10-30 MHz). The quality of the oscillation is typically represented by its quality factor Q defined by the ratio of the peak frequency of the oscillation peak to the width of the oscillation peak at half of the maximum amplitude. In FIG. 1 the relation between the oscillation peak and the quality factor Q is shown. This typically is about 10000 for quartz oscillators. Such oscillators have lateral dimensions on the order of 1 or 2 mm. Integrated oscillators on the other hand, which may e.g. consist of an LC-tank circuit or a miniaturized integrated resonators (RF-MEMS) typically have a much lower quality factor. For integrated oscillators consisting of an LC-tank circuit the quality factor Q typically is smaller than 100, whereas for miniaturized integrated mechanical resonators a quality factor larger than 1000 can be obtained at high frequencies (500 MHz-6 GHz). Nevertheless, the latter require complicated fabrication steps and it is difficult to tune their frequency.
Some applications of the spin torque effect are known. Some aspects of the spin torque effect have been predicted and described in 1996 in for instance patent U.S. Pat. No. 5,659,864. Demonstrations of spin torque have so far been focused on ‘current-induced switching’ for application in Magnetic Random Access Memories. Some examples of the use of spin torque effects are listed below. In S. I. Kiselev et al., Nature 425, 380 (2003), the spin torque effect is studied in a basic structure being a multilayer of 80 nm Cu/40 nm Co/10 nm Cu/3 nm Co/2 nm Cu/30 nm Pt patterned into a nanopillar (elliptical cross section of 130 nm×70 nm) and contacted with a Cu top contact. The 40 nm Co layer acts as the fixed layer, the 10 nm Cu layer is the interlayer and 3 nm Co layer is the excitable layer. The nanopillar embodiment allows to obtain a confined spin polarised charge carrier current.
In W. H. Rippard et al. PRL 92, 027201 (2004), the spin torque effect is studied in a basic structure being a CoFe/Cu/NiFe trilayer that was contacted by patterning a nanohole (diameter 40-100 nm) in the isolator on top. Oscillations were obtained with a frequency that was tuneable between 5 and 35 GHz, depending on the value of the external magnetic field. The modes of most interest are those with very high Q-factor oscillations. The largest observed Q of 18000 was obtained in a nanohole for a magnetic field of 1 T applied at an angle of 30° from the surface and a current of 6 mA, resulting in a frequency of 35.4 GHz. Reasonably high quality factors, but with higher output powers, could be reached at low magnetic fields, e.g. Q=2705 at 0.15 T applied at 85° to the surface, corresponding to a frequency of 9.69 GHz. FIG. 2a illustrates the frequency spectrum of the AC voltage measured over a trilayer contacted through a 40 nm nanohole when a current of 6 mA is sent through and an external field H of 0.15 T is applied at an angle of 85 degrees from the surface, as indicated in the inset. The peak frequency can be set by the external magnetic field in a broad range of 5-35 GHz and with a slope of 26.2 GHz per Tesla as seen in FIG. 2b. The current can also be used to set and control the frequency with a slope of −0.23 GHz per mA, as shown in FIG. 2c. 
Some basic geometries that are used in the state-of-the-art geometries of the current induced oscillator tunable by an external magnetic bias field H, are shown by the devices 100 in FIG. 3. The external magnetic bias field H might be oriented along any direction. Two typical examples, i.e. the nanopillar embodiment and the nanohole embodiment, both allowing confinement of the current, are illustrated in FIG. 3. The diameter of the nanopillar or nanohole is typically small to guarantee a high degree of confinement of the DC current. The systems comprise a so-called trilayer, which exists of a ferromagnetic exitable layer 102, an interlayer 110 and a fixed layer 112. This trilayer might be patterned into a nanopillar or contacted through a nanohole to confine the current and increase the spin torque exerted on the excitable layer. Current is applied through electrodes 116.
The external, i.e. not integrated or united, electromagnet that is currently used requires external not-integrated components. This makes the device large in size, heavy and unpractical.
There is a need to provide fully integrated RF circuits, in which all essential elements for selecting a frequency or tuning a frequency of the oscillations are present in a united way, i.e. structurally or functionally, and which furthermore are able to set or tune the peak frequency of the oscillation while keeping the quality factor and the stability of the oscillation maximal, i.e. as high as possible, and with minimal additional power consumption.